1. Field of the Invention
The present invention relates to a process for the preparation of partial oxidation products and/or partial ammoxidation products of at least one olefinic hydrocarbon A′, in which    A) in a first reaction zone A, at least one paraffinic hydrocarbon A is subjected to a partial dehydrogenation and/or oxydehydrogenation with formation of a product mixture A which contains an unconverted amount of at least one hydrocarbon A and at least one olefinic hydrocarbon A′ formed by the partial dehydrogenation and/or oxydehydrogenation,    B) a portion or the total amount of the components contained in the product mixture A and differing from the at least one paraffinic hydrocarbon A and the at least one olefinic hydrocarbon A′ is separated from said product mixture A, if required in a separation zone, to give a product mixture A′, and either the product mixture A or the product mixture A′ is used for feeding an oxidation and/or ammoxidation zone B and, in the oxidation and/or ammoxidation zone B, at least the at least one olefinic hydrocarbon A′ is subjected to a partial oxidation and/or ammoxidation with formation of a product mixture B which contains, as desired product, at least one partial oxidation and/or ammoxidation product B of the at least one olefinic hydrocarbon A′,    C) the desired product is separated from the product mixture B in a working-up zone C and at least a portion of the unconverted at least one paraffinic hydrocarbon A contained in the product mixture B is recycled as paraffinic recycle hydrocarbon A into the reaction zone A and    D) from time to time, in a nonoperating phase, at least a part of the reaction zone A is not operated for the purpose of the partial dehydrogenation and/or oxydehydrogenation of the at least one paraffinic hydrocarbon A.
Partial oxidation products of olefinic hydrocarbons are important intermediates, for example for the preparation of polymers.
In this document, oxydehydrogenation is understood as meaning a dehydrogenation which is forced by the oxygen present and in which no hydrogen is formed in the intermediate stage.
In this document, a paraffinic hydrocarbon is to be understood as meaning a saturated hydrocarbon. In this document, an olefinic hydrocarbon is to be understood as meaning a hydrocarbon which has at least one ethylenically unsaturated double bond (examples are propylene, isobutene and butadiene).
In this document, the paraffinic and the olefinic hydrocarbons contain, as a rule, not more than ten carbon atoms. In this document, the paraffinic and the olefinic hydrocarbons preferably have two, three or four carbon atoms. Preferred paraffinic hydrocarbons in this document are ethane, propane and butanes. In this document, preferred olefinic hydrocarbons are propylene (propene), ethylene (ethene) and butenes. In this document, the preferred partial oxidation and/or ammoxidation products of olefinic hydrocarbons are acrolein, acrylic acid, ethylene oxide, methacrolein, methacrylic acid, propylene oxide, acrylonitrile and methacrylonitrile.
In this document, a complete oxidation of an olefinic hydrocarbon is understood as meaning that all the carbon contained in the olefinic hydrocarbon is converted into oxides of carbon (CO, CO2). In this document, all reactions of an olefinic hydrocarbon with molecular oxygen which differ therefrom are subsumed under the term partial oxidation. The additional involvement of ammonia in the reaction is referred to as ammoxidation.